Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same and, more particularly, to an amorphous silicon thin film transistor-liquid crystal display device (TFT-LCD) in which a gate driving circuit is integrated on an amorphous silicon TFT substrate and a method of manufacturing the same.
Description of the Related Art
In the information society of these days, electronic display devices are more important as information transmission media and various electronic display devices are widely applied for industrial apparatus or home appliances. Such electronic display devices are being continuously improved to have new appropriate functions for various demands of the information society.
In general, electronic display devices display and transmit various pieces of information to users who utilize such information. That is, the electronic display devices convert electric information signals outputted from electronic apparatus into light information signals recognized by users through their eyes.
In the electronic display devices dividing into an emissive display device and a non-emissive display device, the emissive display device displays light information signals through a light emission phenomena thereof and the non-emissive display device displays the light information signals through a reflection, a scattering or an interference thereof. The emissive display device includes a cathode ray tube (CRT), a plasma display panel (PDP), a light emitting diode (LED) and an electroluminescent display (ELD). The emissive display device is called as an active display device. Also, the non-emissive display device, called as a passive display device, includes a liquid crystal display (LCD), an electrochemical display (ECD) and an electrophoretic image display (EPID).
The CRT has been used for a television receiver or a monitor of a computer as the display device for a long time since it has a high quality and a low manufacturing cost. The CRT, however, has some disadvantages such as a heavy weight, a large volume and high power dissipation.
Recently, the demand for a new electronic display devices is greatly increased such as a flat panel display device having excellent characteristics that thin thickness, light weight, low driving voltage and low power consumption. Such flat panel display devices can be manufactured according to the rapidly improved semiconductor technology.
In the flat panel devices, a liquid crystal display (LCD) device has been widely utilized for various electronic devices because the LCD device has a thin thickness, a low power dissipation and high display quality approximately identical to those of the CRT. Also, the LCD device can be operated under a low driving voltage and can be easily manufactured so that the LCD device is widely used for various electronic apparatuses.
The LCD comprises two substrates, each of the substrates having an electrode, and a liquid crystal layer interposed therebetween. In the LCD, a voltage is applied to the electrodes to realign liquid crystal molecules and control an amount of light transmitted through the molecules.
Among the LCDs, there is mainly used a device including electrodes formed on each of two substrates and a thin film transistor for switching a voltage applied to each of the electrodes. Generally, the thin film transistor is formed on one of the two substrates.
The LCD device utilizing the thin film transistor in a pixel region is divided into an amorphous type TFT-LCD and a polycrystalline type TFT-LCD. The polycrystalline silicon TFT-LCD device has low consumption power and cost, but the TFT manufacturing process is complicated as compared to that of the amorphous silicon TFT-LCD device. Accordingly, the polycrystalline silicon TFT-LCD is mainly used for a small-sized display such as IMT-2000 mobile phone. The amorphous silicon TFT-LCD is suitable for a large-sized display and has a high yield, so is used for display having a large screen such as a notebook PC, an LCD monitor, a high definition television (HDTV) receiver, etc.
As shown in FIG. 1, in a polycrystalline silicon TFT-LCD device, a data driving circuit 12 and a gate driving circuit 14 are formed on a glass substrate 10 on which pixel arrays are formed. A terminal 16 is connected to an integrated printed circuit board (PCB) 20 through a film cable 18. This structure can cut down manufacturing cost and minimize the power loss by integrating the driving circuits.
However, as shown in FIG. 2, in an amorphous silicon TFT-LCD device, a data driving chip 34 is formed on a flexible PCB 32 by a chip on film (COF) method and a data PCB 36 is connected to a data line terminal of pixel array through the flexible PCB 32. Further, a gate driving chip 40 is formed on a flexible PCB 38 by the COF method, and a gate PCB 42 is connected to a gate line terminal of pixel array through the flexible PCB 38.
A recently suggested method is an integrated PCB technology wherein a gate power supply is mounted on a data PCB to thereby eliminate a gate PCB. In a Korea Patent Laid-Open Publication Number 2000-66493, there is disclosed an LCD module adopting an integrated PCB from which the gate PCB is removed.
However, even if the integrated PCB is adopted, a flexible PCB on which a gate driving circuit is formed is still used. Accordingly, since a process of assembling a plurality of flexible PCBs on a glass substrate is carried out in the manufacture of amorphous silicon TFT-LCD, an outer lead bonding (OLB) process is more complicated as compared to the polycrystalline silicon TFT-LCD, thereby raising the manufacturing cost.
Therefore, for the amorphous silicon TFT-LCD, it is demanded a method where the driving circuits and the pixel array are simultaneously formed on the substrate to thereby decrease the number of the assembly process in the same manner of the polycrystalline silicon TFT-LCD.